Forces in Fluids
Teacher's Guide
Editors:
Brian A. Jerome, Ph.D.
Stephanie Zak Jerome
Assistant Editors:
Anneliese Brown
Louise Marrier
Graphics:
Lyndsey Canfield
Dean Ladago
Fred Thodal
Visual Learning Company
www.visuallearningco.com
1-800-453-8481
25 Union Street
Brandon VT 05733
A Message from our Company . . .
Visual Learning is a Vermont-based, family-owned company specializing in the
creation of science programs. As former classroom science teachers we have
designed our programs to meet the needs and interests of both students and
teachers. Our mission is to help educators and students meet educational goals
while experiencing the thrill of science!
Viewing Clearances
The video and accompanying teacher’s guide are for instructional use only. In showing
these programs, no admission charges are to be incurred. The programs are to be
utilized in face-to-face classroom instructional settings, library settings, or similar
instructional settings.
Duplication Rights are available, but must be negotiated with the Visual Learning
Company.
Television, cable, or satellite rights are also available, but must be negotiated with
the Visual Learning Company.
Closed circuit rights are available, and are defined as the use of the program
beyond a single classroom but within a single campus. Institutions wishing to utilize
the program in multiple campuses must purchase the multiple campus version of the
program, available at a slightly higher fee.
Video streaming rights are available and must be negotiated with the Visual Learning
Company.
Discounts may be granted to institutions interested in purchasing programs in large
quantities. These discounts may be negotiated with the Visual Learning Company.
Use and Copyright:
The purchase of this video program entitles the user the right to reproduce or
duplicate, in whole or in part, this teacher’s guide and the black line master handouts
for the purpose of teaching in conjunction with this video, Forces in Fluids. The right
is restricted only for use with this video program. Any reproduction or duplication, in
whole or in part, of this guide and student masters for any purpose other than for use
with this video program is prohibited.
The video and this teacher’s guide are the exclusive property of the copyright
holder. Copying, transmitting, or reproducing in any form, or by any means,
without prior written permission from the copyright holder is prohibited (Title 17,
U.S. Code Sections 501 and 506).
Copyright © 2008
ISBN 9781592342419
Page
2
Forces in Fluids
Visual Learning Company 1-800-453-8481
Table of Contents
Visual Learning Company 1-800-453-8481
A Message from our Company
2
Viewing Clearances
2
Use and Copyright
2
National Standards Correlations
4
Student Learning Objectives
5
Assessment
6
Introducing the Program
7
Program Viewing Suggestions
7
Video Script
8
Answer Key to Student Assessments
12
Answer Key to Student Activities
13
Pre-Test
14
Post-Test
16
Video Review
18
Vocabulary
19
Writing Activity
20
Experimenting with Pressure
21
Make a Barometer
22
Density and Buoyancy
24
Forces in Fluids
Page
3
National Standards Correlations
Benchmarks for Science Literacy
(Project 2061 - AAAS)
Grades 3-5
The Physical Setting - The Earth (4B)
By the end of 5th grade, students should know that:
• Air is a substance that surrounds us, takes up space, and whose movement we feel as wind.
By the end of 8th grade, students should know that:
• The earth is mostly rock. Three-fourths of its surface is covered by a relatively thin layer
of water (some of it frozen), and the entire planet is surrounded by a relatively thin
blanket of air. It is the only body in the solar system that appears able to support
life.
The Physical Setting - The Structure of Matter (4D)
By the end of 8th grade, students should know that:
• Atoms and molecules are perpetually in motion. Increased temperature means greater
average energy of motion, so most substances expand when heated. In solids,
the atoms are closely locked in position and can only vibrate. In liquids, the atoms or
molecules have higher energy of motion, are more loosely connected, and can slide
past on another; some molecules may get enough energy to escape into a gas.
In gases, the atoms or molecules have still more energy of motion and are free of one
another except during occasional collisions.
National Science Education Standards
(Content Standards: K-4, National Academy of Sciences)
Physical Science - Content Standard B
As a result of their activities in grades K-4, all students should develop an understanding of:
Properties of Objects and Materials
• Objects have many observable properties, including size, weight, shape, color,
temperature, and the ability to react with other substances. Those properties can be
measured using tools, such as rulers, balances, and thermometers.
As a result of their activities in grades 5-8, all students should develop an understanding of:
Properties and Changes of Properties of Matter
• A substance has characteristic properties, such as density, a boiling point, and solubility,
all of which are independent of the amount of the sample. A mixture of substances often
can be separated into the original substances using one or more of the characteristic
properties.
Page
4
Forces in Fluids
Visual Learning Company 1-800-453-8481
Student Learning Objectives
Upon viewing the video and completing the enclosed student activities, students will
be able to do the following:
• Define fluids as substances that can easily flow and readily change shape.
• Explain that fluids flow because particles can easily move past each other.
• Understand that particles in fluids exert pressure equally in all directions.
• Describe how fluids move from areas of higher pressure to areas of lower pressure.
• Explain that the atmosphere around us creates pressure, referred to as air pressure.
• Understand Pascal’s principle, which states that when a force is applied to a confined
fluid, an increase in pressure is transmitted equally to all parts of the fluid.
• Describe how hydraulic devices utilize Pascal’s principle to transmit pressure from one
point to another.
• Provide an example of a buoyant force at work.
• Define the term “density.” State the formula for computing density:
Density=Mass/Volume.
• Cite an example of an object that is less dense than water, causing it to float, and an
object that is denser than water, causing it to sink.
• Understand Bernoulli’s principle, which states, that a moving stream of fluid has a lower
pressure than the pressure in the surrounding fluid.
Visual Learning Company 1-800-453-8481
Forces in Fluids
Page
5
Assessment
Preliminary Test (p. 14-15):
The Preliminary Test is an assessment tool designed to gain an
understanding of students’ preexisting knowledge. It can also be used as a
benchmark upon which to assess student progress based on the objectives
stated on the previous pages.
Post-Test (p. 16-17):
The Post-Test can be utilized as an assessment tool following student
completion of the program and student activities. The results of the
Post-Test can be compared against the results of the Preliminary Test to
assess student progress.
Video Review (p. 18):
The Video Review can be used as an assessment tool or as a student
activity. There are two sections. The first part contains questions displayed
during the program. The second part consists of a five-question video quiz
to be answered at the end of the video.
Page
6
Forces in Fluids
Visual Learning Company 1-800-453-8481
Introducing the Program
Before showing the video program to students, do the following demonstration.
Hold a balloon up in front of the class. Ask students what needs to be done to
inflate the balloon. Next, ask them to predict how the balloon will inflate when
it is blown into. Will it form unevenly? Will there be bulges? After discussing
their predictions, blow up the balloon. Have students closely observe the
process of inflating the balloon.
After inflating the balloon, ask students to describe their observations. Ask
them if all sides of the balloon expanded evenly or unevenly. Next, have a
student push in on one side of the balloon. Observe what happens to the
entire balloon. Write the term “Pascal’s principle” on the board. Tell students
to pay close attention to the video to see how Pascal’s principle explains why
the balloon inflated the way it did.
Program Viewing Suggestions
The student master “Video Review” (p.18) is provided for distribution to
students. You may choose to have your students complete this master while
viewing the program or do so upon its conclusion.
The program is approximately 14 minutes in length and includes a five-question
video quiz. Answers are not provided to the Video Quiz in the video, but are
included in this guide on page 12. You may choose to grade student quizzes
as an assessment tool or to review the answers in class.
The video is content-rich with numerous vocabulary words. For this reason you
may want to periodically stop the video to review and discuss new terminology
and concepts.
Visual Learning Company 1-800-453-8481
Forces in Fluids
Page
7
Video Script
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
Page
If you have ever taken a ride in a plane,…
…watered your garden with a hose,…
…or swam underwater, you have experienced forces in fluids.
What are some of the characteristics of forces and fluids?
And, how do they affect our everyday lives?
During the next few minutes we are going to explore these questions and others…
… as we investigate forces in fluids.
Graphic Transition – Fluids and Pressure
Every time you take a breath of air…
…or take a bath, you are using fluids.
So, what exactly is a fluid? A fluid is a substance that can easily flow.
Fluids can also readily change shape. Both liquids and gases have this characteristic.
Fluids are made of particles too small to be seen with the naked eye.
They flow because particles can easily move past each other.
Particles in fluids are constantly moving. As they collide with a surface, they exert a
force on that surface.
You Decide! Describe how the particles inside this balloon exert force.
The particles exert pressure on the walls of the balloon, pushing them outward.
The push or force that particles exert over an area is called pressure.
Fluid pressure is exerted equally in all directions.
Another characteristic of fluids is that they move from areas of higher pressure to
areas of lower pressure.
When a can of soda is opened, you hear a loud pop. This is because gas is rushing
from an area of high pressure to an area of low pressure.
And in this dropper, water is released as pressure is increased by squeezing on the
bulb.
Graphic Transition – Variations in Pressure
Even though you can’t feel it, the atmosphere around you is exerting tremendous
pressure on your body.
You can’t feel the pressure because fluids inside your body balance the pressure
outside your body.
The pressure created by the atmosphere above and around us is called air pressure.
Air pressure can vary depending on your location.
For example, the air pressure at sea level is much greater...
...than the air pressure here in the mountains. This is because there is less
atmosphere overhead in the mountains than at sea level.
In fact, air pressure at the top of Mt. Everest is only about…
…one third of the air pressure at sea level.
Pressure also varies with water depth.
As depth increases, water pressure increases.
8
Forces in Fluids
Visual Learning Company 1-800-453-8481
Video Script
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
If you have ever dove deep underwater, you may have noticed the pressure increase.
This is because the water above you was exerting a downward force.
These are just a couple of examples of variations in pressure of fluids.
Graphic Transition – Pascal’s Principle
Watch what happens when this stopper is pressed down on this bottle full of water.
The water squirts up!
The pressure applied to the water by the stopper acts equally in all directions,
including up!
In the 1600s, a French mathematician by the name of Blaise Pascal made a similar
observation.
Pascal’s principle states that when a force is applied to a confined liquid, an increase
in pressure is transmitted equally to all parts of the fluid.
Pascal’s principle is used in many helpful machines and products today.
For example, hydraulic systems take advantage of Pascal’s principle.
Hydraulic devices, such as those in heavy equipment, use liquids to transmit pressure
from one point to another.
The brakes on most cars use hydraulic devices to multiply forces.
When the brake pedal is pushed downward, a piston is engaged.
The piston exerts pressure on a type of fluid called brake fluid.
Pascal’s principle tells us that this pressure is transmitted equally to all parts of the
liquid-filled brake system.
Pressure is then transmitted through the brake lines to larger pistons within the
wheels, these in turn push brake pads against the brake discs.
Friction created between the brake pads and the brake discs causes the car to slow
down.
Thanks to Pascal’s principle, a fast-moving car can be stopped with the touch of a
foot!
Graphic Transition – Buoyancy and Density
You Predict! What will happen when this rubber duck is pushed underwater and then
released?
It pops back up to the surface.
The force that pushes the duck to the top of the water is called buoyant force.
Buoyancy is the upward force exerted by a fluid on a submerged object due to
differences in pressure.
This diagram illustrates an object in water. The weight of the object causes it to move
downward into the liquid.
Fluid pressure also exerts a buoyant, or upward, force, on the object. In this case, the
upward force generally balances the downward force, causing it to float.
If the downward force is less than the buoyant force, the object will accelerate
upward.
Visual Learning Company 1-800-453-8481
Forces in Fluids
Page
9
Video Script
60. But, if the downward force or weight of an object is greater than the buoyant force, the
object will sink.
61. One factor that influences the buoyancy of objects is their density.
62. You Decide! Why does this rock sink while this rubber cork floats?
63. The rock sinks because it is denser than water. The cork, on the other hand, is less
dense than water, so it floats.
64. What exactly is density?
65. Density is a physical property of matter. More specifically, it is the amount of mass in
an object per unit of volume.
66. You can think of density as the amount of mass packed into a given space.
67. The density of water is 1.0 gram per cubic centimeter.
68. Objects with a density greater than 1.0 gram per cubic centimeter, such as this nail,
sink.
69. But objects with a density less than 1.0 gram per cubic centimeter, such as this pencil,
float.
70. Graphic Transition – Fluids in Motion
71. You Predict! What do you think will happen to this ball when it comes in contact with
this stream of air?
72. Instead of being pushed away, the ball is held in the moving stream of air. Why?
73. The ball is drawn to the rapidly moving stream of air because the stream has a lower
pressure than the surrounding air.
74. The Bernoulli principle states that the pressure in a moving stream of fluid is less
than the pressure in the surrounding fluid.
75. The Bernoulli principle explains in part why smoke rises up a chimney.
76. Wind blowing across the top of a chimney has a lower pressure than the surrounding
air.
77. The smoke moves from the bottom of the chimney, an area of high pressure, to the
top of the chimney, an area of low pressure.
78. The Bernoulli principle also helps planes fly.
79. The wings of aircraft are designed so that air moves at different speeds above and
below the wing. This creates differences in pressure, which produces lift.
80. Graphic Transition – Summing Up
81. During the past few minutes, we have explored the topic of forces in fluids.
82. We learned that fluids are substances that can easily flow and change shape.
83. Both gases and liquids have these characteristics.
84. We saw that fluids exert a force over an area called pressure.
85. And we learned that fluids move from areas of high pressure to areas of low pressure.
86. Variations in pressure due to elevation and depth were described.
87. We discussed Pascal’s principle, which states that when a force is applied to a confined
liquid, an increase in pressure is transmitted equally to all parts of the fluid.
Page
10
Forces in Fluids
Visual Learning Company 1-800-453-8481
Video Script
88.
89.
90.
91.
The application of Pascal’s principle in hydraulic devices was demonstrated.
We briefly discussed the forces involved in the buoyancy of objects.
And we saw how density affects buoyancy.
Finally, we explored the Bernoulli principle, which states that the pressure in a moving
stream of fluid is less than the pressure in the surrounding fluid.
92. So, the next time you swim underwater...
93. ...or ride in a plane,...
94. ...think about some of the things we have discussed during the past few minutes.
95. You just might think about forces in fluids a little differently.
96. Graphic Transition – Video Assessment
Fill in the correct word to complete the sentence. Good luck and let’s get started.
1. The force that particles in fluid exert over an area is called ___________.
2. Fluids move from areas of high pressure to areas of ________ pressure.
3. Hydraulic systems take advantage of _________ principle.
4. __________ is the upward force of a fluid on a submerged object.
5. An object that is denser than water will __________.
Visual Learning Company 1-800-453-8481
Forces in Fluids
Page
11
Answer Key to Student Assessments
Pre-Test (p. 14-15)
Post-Test (p. 16-17)
1. c - flow
2. a - particles
3. d - pressure
4. b - low pressure
5. c - air pressure
6. a - equally
7. d - buoyancy
8. a - density
9. c - greater
10. a - Bernoulli’s principle
11. false
12. true
13. true
14. false
15. false
16. A fluid is a substance that can easily
flow and change shape.
17. Water, juice, milk, gasoline, motor oil,
and soda are examples of fluids.
18. Pressure is the force applied to an area.
19. Buoyancy is the upward force of a fluid
on a submerged object due to differences in
pressure.
20. Rocks sink because they have a greater
density than water.
1. a - density
2. c - air pressure
3. a - particles
4. c - greater
5. b - low pressure
6. a - Bernoulli’s principle
7. d - pressure
8. c - flow
9. d - buoyancy
10. a - equally
11. true
12. false
13. false
14. true
15. false
16. Rocks sink because they have a greater
density than water.
17. Buoyancy is the upward force of a fluid
on a submerged object due to differences in
pressure.
18. Water, juice, milk, gasoline, motor oil,
and soda are examples of fluids.
19. Pressure is the force applied to an area.
20. A fluid is a substance that can easily
flow and change shape.
Video Review (p. 18)
1. The particles exert pressure on the walls of the balloon, pushing them outward.
2. The rubber duck pops back up to the surface when it is pushed underwater and then
released.
3. The rock sinks because it is denser than water. The cork floats because it is less dense
than water.
4. The ball is held in the moving stream of air.
1.
2.
3.
4.
5.
Page
The force that particles in fluid exert over an area is called pressure.
Fluids move from areas of high pressure to areas of low pressure.
Hydraulic systems take advantage of Pascal’s principle.
Buoyancy is the upward force of a fluid on a submerged object.
An object that is denser than water will sink.
12
Forces in Fluids
Visual Learning Company 1-800-453-8481
Answer Key to Student Activities
Vocabulary (p. 19 )
Make a Barometer (p. 22-23 )
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
1. Pressure is a force that particles exert over an
area.
2. Air pressure is the force (pressure) created by
the atmosphere above and around us.
3. The air pressure at a specific location can
change due to atmospheric changes. High and low
pressure weather systems account for changes in
air pressure at Earth’s surface.
4. A barometer is an instrument used to measure
air pressure.
5. The stretched balloon reacted to changes in air
pressure. In turn, the straw was attached to the
balloon, causing it to also move.
6. Answers will vary.
7. The student-made barometer only reacts to
changes in air pressure and does not provide an
absolute value of barometric pressure. Also, the
balloons lose their elasticity over time.
fluid
pressure
air pressure
Pascal’s principle
hydraulic systems
buoyancy
density
1.0 g/cm³
float
Bernoulli’s principle
Writing Activity (p. 20)
Every time you take a breath of air or a drink of water,
you are using fluids. A fluid is a substance that
can easily flow. Particles in fluids are constantly
moving. As particles collide with a surface, they exert
a force on the surface, referred to as fluid pressure.
The pressure created by the atmosphere above
and around us is called air pressure. Pressure
varies with water depth. As depth increases, water
pressure increases. Pascal’s principle states
that when a force is applied to a confined liquid, an
increase in pressure is transmitted equally to all
parts of the fluid. This principle is used in hydraulic
systems, which use liquids to transmit pressure
from one point to another. Heavy equipment and the
brakes in cars use hydraulic systems.
In Your Own Words (p. 20 )
1. A fluid is a substance that can easily flow and
change shape. Gases and liquids are fluids.
2. Water pressure increases with depth. As you
swim deeper, a greater amount of water is above
you therefore pressure increases.
3. Rocks are more dense than water and therefore
they sink. Sponges are less dense than water and
therefore float.
Experimenting with Pressure (p. 21 )
1. The bottom stream flowed the strongest. The
top hole had the weakest stream of water.
2. The bottom stream was strongest because
it had the greatest pressure. The pressure was
greater at the bottom of the container because
there was more water on top of it.
3. Water pressure from inside the can forced the
can to rotate as it escaped through the holes. The
holes were angled, causing the can to rotate as
water streamed outward.
Visual Learning Company 1-800-453-8481
Density and Buoyancy (p. 24-25 )
The density for each object:
wooden block: < 1.0 g/cm³
stone: > 1.0 g/cm³
sponge: < g/cm³
piece of cardboard: < g/cm³
piece of plastic: < g/cm³
piece of metal: > 1.0 g/cm³
1. Buoyancy is the upward force exerted by a
fluid on a submerged object due to differences in
pressure.
2. Density is the amount of matter per unit volume.
Objects with a density greater than 1.0 g/cm³ sink,
and objects with a density less than 1.0 g/cm³ float.
3. First, find the mass of each object by using a
balance. Next, calculate the volume of the object
(volume = length x height x width). Then divide the
object’s mass by its volume.
4. The wooden block, sponge, piece of cardboard,
and piece of plastic floated.
5. The stone and piece of metal sank. They had a
greater density than water.
Forces in Fluids
Page
13
Pre-Test
Name
Circle the best answer for each of the following questions.
1. A fluid is a substance that can easily:
a. freeze
b. thaw
2. Fluids are made up of many:
a. particles
b. sizes
c. flow
d. break
c. rocks
d. beads
3. The force that particles in a fluid exert over an area is called:
a. effort
b. motion
c. potential energy
d. pressure
4. Fluids move from areas of high pressure to areas of:
a. high pressure
b. low pressure
c. static pressure
d. random pressure
5. The pressure created by the atmosphere above and around us is called:
a. weather
b. auroras
c. air pressure
d. magnetism
6. Pascal’s principle states that when a force is applied to a confined fluid, pressure is
transmitted to all parts of the fluid:
a. equally
b. incrementally
c. unevenly
d. unequally
7. The force that causes objects to float is referred to as:
a. gravity
b. density
c. lift
d. buoyancy
c. weight
d. pressure
8. The amount of mass per unit of volume is:
a. density
b. volume
9. The density of a rock, compared to the density of water, is:
a. less
b. equal
c. greater
d. the same
10. This principle states that the pressure in a moving stream of fluid is less than the pressure
in the surrounding fluid.
a. Bernoulli’s
principle
b. kinetic energy
c. quantum theory
d. Pascal’s
principle
Forces in Fluid
Visual Learning Company
Page
14
Pre-Test
Name
Write true or false next to each statement.
11.
Liquids and gases are not considered fluids.
12.
Fluids flow because their particles move easily past each other.
13.
Air pressure can vary depending on your location.
14.
Water pressure is the same at the bottom of the ocean as at
the surface.
15.
The density of an object has no effect on buoyancy.
Write a short answer for each of the following.
16. What is a fluid?
17. List two examples of fluids.
18. What is pressure?
19. What is buoyancy?
20. Why do rocks sink?
Forces in Fluid
Visual Learning Company
Page
15
Post-Test
Name
Circle the best answer for each of the following questions.
1. The amount of mass per unit of volume is:
a. density
b. volume
c. weight
d. pressure
2. The pressure created by the atmosphere above and around us is called:
a. weather
b. auroras
3. Fluids are made up of many:
a. particles
b. sizes
c. air pressure
d. magnetism
c. rocks
d. beads
4. The density of a rock, compared to the density of water, is:
a. less
b. equal
c. greater
d. the same
5. Fluids move from areas of high pressure to areas of:
a. high pressure
b. low pressure
c. static pressure
d. random pressure
6. This principle states that the pressure in a moving stream of fluid is less than the pressure
in the surrounding fluid:
a. Bernoulli’s
principle
b. kinetic energy
c. quantum theory
d. Pascal’s
principle
7. The force that particles in a fluid exert over an area is called:
a. effort
b. motion
c. potential energy
d. pressure
c. flow
d. break
8. A fluid is a substance that can easily:
a. freeze
b. thaw
9. The force that causes boats to float is referred to as:
a. gravity
b. density
c. lift
d. buoyancy
10. Pascal’s principle states that when a force is applied to a confined fluid, pressure is
transmitted to all parts of the fluid:
a. equally
b. incrementally
c. unevenly
d. unequally
Forces in Fluid
Visual Learning Company
Page
16
Post-Test
Name
Write true or false next to each statement.
11.
Air pressure can vary depending on your location.
12.
The density of an object has no effect on buoyancy.
13.
Liquids and gases are not considered fluids.
14.
Fluids flow because their particles move easily past each other.
15.
Water pressure is the same at the bottom of the ocean as at
the surface.
Write a short answer for each of the following.
16. Why do rocks sink?
17. What is buoyancy?
18. List two examples of fluids.
19. What is pressure?
20. What is fluid?
Forces in Fluid
Visual Learning Company
Page
17
Video Review
Name
While you watch the video, answer these questions:
1. You Decide!
Describe how the particles inside this balloon exert force.
2. You Predict!
What will happen when this rubber duck is pushed underwater and then released?
3. You Decide!
Why does this rock sink while this rubber cork floats?
4. You Predict!
What do you think will happen to this ball when it comes in contact with this stream of
air?
After you watch the video, test your knowledge with these questions.
1. The force that particles in fluid exert over an area is called _______________.
2. Fluids move from areas of high pressure to areas of ____________ pressure.
3. Hydraulic systems take advantage of _______________ principle.
4. ______________ is the upward force of a fluid on a submerged object.
5. An object that is denser than water will _______________.
Forces in Fluid
Visual Learning Company
Page
18
Vocabulary
Name
Use these words to fill in the blanks next to the sentences below.
Words
fluid
Bernoulli’s principle
pressure
air pressure
hydraulic systems
density
Pascal’s principle
buoyancy
1.0 g/cm³
float
1.
A substance that can easily flow and readily change shape.
2.
The force exerted by particles over an area.
3.
The pressure created by the atmosphere.
4.
States that when a force is applied to a confined fluid, an
increase in pressure is transmitted equally to all parts of the
fluid.
5.
Devices used in equipment that take advantage of Pascal’s
principle; most brakes use these systems.
6.
The upward force exerted by a fluid on a submerged object due
to differences in pressure.
7.
The amount of mass per unit of volume; a factor that influences
the buoyancy of an object.
8.
The density of water.
9.
Objects possessing a density of less than 1.0 g/cm³ will do this
in water.
10.
States that the pressure in a moving stream of fluid is less than
that in the surrounding fluid.
Forces in Fluid
Visual Learning Company
Page
19
Writing Activity
Words
hydraulic systems
particles
Name
air pressure
increases
equally
flow
fluid pressure
Pascal’s principle
fluids
Use the correct word from above to complete the sentences in the following paragraph.
Every time you take a breath of air or a drink of water, you are using __________________. A
fluid is a substance that can easily __________________. __________________in fluids are
constantly moving. As particles collide with a surface, they exert a force on the surface, referred
to as _______________________. The pressure created by the atmosphere above and around
us is called __________________. Pressure varies with water depth. As depth increases,
water pressure __________________. __________________ states that when a force is
applied to a confined liquid, an increase in pressure is transmitted __________________ to all
parts of the fluid. This principle is used in __________________, which use liquids to transmit
pressure from one point to another. Heavy equipment and the brakes in cars use hydraulic
systems.
In Your Own Words
1. What is a fluid? Identify two types of fluids.
2. Why do you feel more pressure as you swim deeper?
3. Why do rocks sink and sponges float?
Forces in Fluid
Visual Learning Company
Page
20
Experimenting
with Pressure
Name
Background: At some point you have probably taken a deep breath and dove to the bottom of
a pool. When you approached the bottom, you may have noticed pressure pushing on all parts
of your body. Pressure is the push or force that particles exert over an area. When you were
diving, pressure was created by particles of water exerting a force on the body. In the case of
water, pressure increases as depth increases. Can you imagine how great the water pressure
is at the bottom of the ocean? In the deepest part of the ocean, water pressure is so great it can
crush a car. In this activity, you will experiment with pressure.
Materials: cardboard/plastic milk or juice container, nail, aluminum soda can, string
Directions:
1. Work in groups of two or three. Obtain a milk or juice container and a nail.
2. Using a nail, carefully poke three holes in the side of the container. Space the holes
evenly apart from top to bottom. If you don’t feel comfortable doing this, ask your instructor
to poke the holes with the nail.
3. While holding the container over the sink, fill it quickly with water to the top.
4. Observe what happens. Does each stream of water coming out of the holes look the
same?
5. For the next part of the activity, obtain a soda can, a nail, and a piece of string.
6. Using the nail, carefully make a hole in the side of the can about one centimeter up from
the bottom. Carefully push the nail straight in and then twist the nail until it makes a
right angle. If you don’t feel comfortable poking holes in the can with the nail, ask
your teacher for assistance.
7. Make two other holes in the can spaced evenly apart.
8. Tie the string to the top of the can.
9. Submerge the can in a container of water until it fills to the top with water.
10. Quickly lift the can and observe what happens.
Questions:
1. Describe how the streams of water differed from each other in the first part of the activity.
2. What caused the streams of water to differ from each other?
3. Explain why the can rotated in the second part of the activity.
Forces in Fluid
Visual Learning Company
Page
21
Make a
Barometer
Name
Background: Even though you can’t feel it, the atmosphere around you is exerting
tremendous pressure on your body. You can’t feel the pressure because fluids
inside your body balance the pressure outside your body. The pressure created by
the atmosphere above and around us is called air pressure. Air pressure can vary
depending on your location. For example, air pressure at sea level is much greater than
air pressure high in the mountains. This is because there is less atmosphere overhead
in the mountains than at sea level. In fact, air pressure at the top of Mt. Everest is only
about one third of the air pressure at sea level.
Pressure also varies at the same location on Earth’s surface due to changes in the
atmosphere. Perhaps you have heard of high and low pressure weather systems.
These systems are constantly forming and moving in the atmosphere, changing the
air pressure at the surface. A device called a barometer measures air pressure.
Barometers help meteorologists understand and predict the weather. Scientists,
meteorologists, and avid weather enthusiasts use very accurate barometers. In this
activity you will make your own simple barometer.
Materials:
empty metal can
balloon
plastic spoon
petroleum jelly
tape
straw
piece of paper
Directions:
1. Work with a partner in this activity.
2. Use a plastic spoon to carefully spread a thin layer of petroleum jelly around the
edge of a metal can. Be careful not to cut yourself on the can!
3. Gently stretch the mouth of the balloon across the top of the can.
4. Tape a straw flat on the middle of the balloon. Leave about half of the straw
extending out flat beyond the can.
5. Tape a piece of paper against the wall where it will not be disturbed, such as above a
shelf or windowsill.
Forces in Fluid
Visual Learning Company
Page
22
Make a
Barometer
Name
5. Place the can and straw apparatus next to the paper. Mark the end of the straw on
the paper.
6. Every day check the position of the straw on your barometer. Mark the new position
of the straw each day. Write the date next to the mark.
7. Answer the following questions.
Questions:
1. What is pressure?
2. What is air pressure?
3. What causes air pressure to change from day to day at the same location?
4. What is a barometer?
5. In the barometer you made, what part of the instrument moved as air pressure changed?
6. Describe how air pressure changed over several days.
7. What are the shortcomings of the barometer you made?
Forces in Fluid
Visual Learning Company
Page
23
Density and
Buoyancy
Name
Background: Have you ever noticed that when you throw a dry stick into the water, it usually
floats? Have you noticed that it does not matter how big the stick is, it always floats? In fact,
huge logs even float. Why? The reason has to do with something called buoyancy. Buoyancy
is the upward force exerted by a fluid on a submerged object due to differences in pressure.
The weight of an object causes it to move downward into a liquid. Fluid pressure also exerts
a buoyant, or upward, force on the object. If the upward force balances the downward force,
an object floats. If the downward force is less than the buoyant force, an object will accelerate
upward. But, if the downward force or weight of an object is greater than the buoyant force, the
object sinks. One factor that influences the buoyancy of objects is density.
Density is a physical property of matter. Density is the amount of matter per unit of volume.
Another way to think about density is that it is the amount of stuff (matter) that is packed into a
space (volume). The more matter packed into a space, the denser the object.
Different objects tend to have different densities. For example, a rock has a greater density than
a sponge. Density is often described or measured in grams per cubic centimeters. The density
of water is 1.0 gram per cubic centimeter. Objects with a density greater than 1.0 gram per
cubic centimeter sink in water. Objects with a density less than 1.0 gram per cubic centimeter
float in water. In this activity you will calculate the density of various objects and predict if they
will float or sink.
Materials: Density Data Table, metric ruler, balance, calculator, square or rectangular wooden
block, square or rectangular stone, square or rectangular sponge, square or rectangular piece
of cardboard, square or rectangular piece of plastic, square or rectangular piece of metal,
container of water
Directions:
1. Work with a partner to calculate the density of each object and predict if the object will float
or sink in water.
2. It is a simple process to calculate the density of objects. As we stated, density is the amount
of mass per unit of volume. In other words, Density = Mass/Volume.
3. To calculate density, you must first determine the mass and volume.
4. First you will find the mass of each object. Use a balance to calculate the mass of each
object. Your teacher will instruct you how to use a balance.
5. Record the mass of each object in the data table.
6. Next, you must compute the volume of each object. It is easy to calculate the volume of
regularly-shaped solids. Measure the length, height, and width of each object, and then multiply
all three. Volume = length x height x width
7. Find the volume of each object and record it in the data table.
8. To calculate the density of each object, divide its mass by its volume. The units you will end
up with are expressed in grams per cubic centimeter, or g/cm³
Forces in Fluid
Visual Learning Company
Page
24
Density and
Buoyancy
Name
9. Next, predict if the object will sink or float in water. Remember, objects with a density of
greater than 1.0 gram per cubic centimeter sink, and objects with a density of less than 1.0 gram
per cubic centimeter float.
10. Finally, place each object in water to test your predictions.
Density Data Table
OBJECT
MASS
VOLUME
DENSITY g/cm³
TEST RESULT
SINK OR FLOAT
Wooden block
Stone
Sponge
Piece of
cardboard
Piece of plastic
Piece of metal
Questions:
1. What is buoyancy?
2. What is density and how does it affect buoyancy in water?
3. How did you calculate the density of objects in this activity?
4. What objects floated?
5. List the objects that sank. How did their densities compare to the density of water?
Forces in Fluid
Visual Learning Company
Page
25